For the amount of chemicals in this colour, I don't think it really matters if you shampoo once after colouring. Any kind of color will disrupt the hair shaft somewhat. That means you've had to do some kind of 'damage' to the natural oil layer on top of the hair cuticle.

So if you are wanting to stay pure to being CG, you can't really colour treat your hair.

That said, why the heck is it so important? The point of curly girl method is to not damage your hair so much. That is nice, but if you don't like the colour of your hair, I think you can balance that with a tiny bit of damage you will get from a non-lifting gentle hair colour plus one non-sulphate shampoo.